In cellular networks, e.g., LTE (Long Term Evolution) networks as specified by 3GPP (3rd Generation Partnership Project), techniques referred to as dual connectivity and carrier aggregation may be used to enhance bandwidth for radio transmissions between the cellular network and a user equipment (UE). Carrier aggregation is for example specified in 3GPP TS 36.300 V12.1.0 (2014-03), and architectures for implementing dual connectivity are discussed in 3GPP TR 36.842 V12.0.0 (2013-12).
In dual connectivity, the UE is simultaneously connected to multiple cells of the cellular network. In this case, respective base stations of the cells, in the LTE technology referred to as eNB, may individually perform scheduling of transmissions on their respective connection to the UE, which are formed on different carriers. In the case of carrier aggregation, the eNB serving the UE may establish its connection to the UE using multiple pairs of downlink (DL) carriers and uplink (UL) carriers.
UL power control for the LTE physical layer is for example described in Section 5.1 of 3GPP TS 36.213 V.12.0.0 (2013-12). This power control is applied for both an uplink data channel referred to as PUSCH (Physical Uplink Shared Channel) and an uplink control channel referred to as PUCCH (Physical Uplink Control Channel). The principles of UL power control generally involve that the transmit power utilized by the UE on an UL channel is set in such a way that a path loss between the UE and the serving eNB is compensated and thereby a given received signal power for this UL channel is ensured at the serving eNB.
For UL transmissions, a power headroom report (PHR) provided by the UEs may be used to perform link adaptation and scheduling. The PHR indicates the power still available at the UE given the resource allocation decided by the eNB at the time of the report. If the PHR indicates that more power is available at the UE and there is data in the buffer, the eNB may perform link adaptation and scheduling to achieve higher throughput, using this additionally available power.
In some scenarios, the UE may experience a very large path loss, e.g., due to being located close to the cell edge or behind some obstacle. This may adversely affect the UL channels, such as the PUCCH or PUSCH. In particular, such transmissions may in some cases not be possible while at the same time complying with a transmit power budget of the UE.
Further, in a dual connectivity scenario where the different eNBs perform individual scheduling on their respective links to the UE, a lack of coordination between these eNBs may result in problems. In particular, at each of the eNBs, the impact of scheduling or link adaptation performed by the other eNB is typically unknown, which means that the PHR alone does not allow for ensuring compliance with the transmit power budget of the UE. Therefore, suboptimal scheduling or link adaptation by the eNBs may adversely affect the UL channels.
In typical scenarios, at least one UL channel is needed to enable efficient DL transmissions. For example, in the case of carrier aggregation a PUCCH may be required for transmission of UL control information, such as scheduling requests or feedback with respect to DL transmissions. In the case of dual connectivity, a PUCCH may be required between the UE and each of the eNBs to which the UE is connected. If such UL channel is suffering from poor quality, the expected increase in performance due to the utilization of carrier aggregation or dual connectivity may not be achieved. Further, in the case of dual connectivity the sharing of the transmit power budget by multiple eNBs may even result in a degradation as compared to a scenario without dual connectivity, i.e., a single connectivity configuration.
Accordingly, there is a need for techniques which allow for efficiently utilizing different connectivity configurations for a connection to a cellular network.